Plot the decision boundaries of a VotingClassifier for
two features of the Iris dataset.

Plot the class probabilities of the first sample in a toy dataset
predicted by three different classifiers and averaged by the
VotingClassifier.

First, three exemplary classifiers are initialized (DecisionTreeClassifier,
KNeighborsClassifier, and SVC) and used to initialize a
soft-voting VotingClassifier with weights [2, 1, 2], which means that
the predicted probabilities of the DecisionTreeClassifier and SVC
count 5 times as much as the weights of the KNeighborsClassifier classifier
when the averaged probability is calculated.